A number of rare sterane hydrocarbons untypical of younger Phanerozoic petroleum systems have been found by gas chromatography-mass spectrometry in crude oils from the Nepa-Botuoba anteclise of the Siberian platform and the South Oman salt basin of the Arabian platform (Huqf family oils). Among regular steranes, a continuous series of C-21 to C-30 hydrocarbons including the previously unknown C-23-C-25 isomers have been identified. It has been noted that short-chain C-21 and C-22 steranes are represented by the most thermally stable pregnane species diginane and methyldiginane. Another series of steroids is represented by A-norsteranes, the structures demethylated at C10 (main fragment ion in the mass spectrum at m/z 203). Tricyclic hydrocarbons C-26-C-29 identified by m/z 219 have been attributed to the homologous series of 8,14-secosteranes. These chemofossils have a wide stratigraphic range of occurrence and, like modern minor secosterynes, can be associated with lipid membranes of sponge and their bacterial synbiotics.